Torque Transmission Mechanism

The present application is based on, and claims priority from JP Application Serial Number 2024-071258, filed Apr. 25, 2024, the disclosure of which is hereby incorporated by reference herein in its entirety.

The present disclosure relates to a torque transmission mechanism.

With respect to the torque transmission mechanism, JP 2019-132364 A discloses an eccentric oscillation type deceleration mechanism. In the deceleration mechanism disclosed in JP 2019-132364 A, torque transmission is achieved by transmitting a rotation component of an external gear to a carrier body via an inner pin.

With the technique disclosed in JP 2019-132364 A, when the mechanism operates, a load in a shearing direction is applied to the inner pin in charge of the torque transmission, and thus there was a risk that the inner pin was broken.

According to an embodiment of the present disclosure, a torque transmission mechanism is provided. The torque transmission mechanism includes a first member having a cylindrical shape and configured to be rotatable around a rotation axis, the first member including an outer peripheral surface provided with a first groove having a zigzag shape extending around the rotation axis, a second member having an annular shape surrounding the first member and configured to be rotatable around the rotation axis, the second member including an inner peripheral surface provided with a second groove having a zigzag shape extending around the rotation axis, one or more first rolling members disposed in the first groove and in the second groove and configured to be rollable in the first groove and in the second groove, and a first regulating member disposed between the first member and the second member and configured to allow movement of the first rolling members along the rotation axis and regulate movement of the first rolling members around the rotation axis.

is a perspective view illustrating a schematic configuration of a torque transmission mechanismin a first embodiment.is an exploded perspective view illustrating a schematic configuration of the torque transmission mechanism.illustrates arrows representing X, Y, and Z directions orthogonal to each other. The X direction and the Y direction are directions parallel to a horizontal surface, whereas the Z direction is a direction along a vertically upward direction. The arrows representing the X, Y, and Z directions are also illustrated in other drawings as appropriate such that illustration directions correspond to. In the following description, when a direction is specified, a direction indicated by an arrow in each drawing is referred to as “+” and a direction opposite thereto is referred to as “−”, and positive and negative signs are used in combination in direction notation. Hereinafter, a +Z direction is also referred to as “up” and a −Z direction is also referred to as “down”.

In the embodiment, the torque transmission mechanismis configured as a deceleration device. As illustrated in, the torque transmission mechanismincludes a first member, a second member, one or more first rolling members, and a first regulating member. Furthermore, the torque transmission mechanismin the embodiment includes a first bearing portionand a second bearing portion.

The torque transmission mechanismin the embodiment has a cylindrical shape as a whole. The torque transmission mechanismis disposed such that a rotation axis AX of the torque transmission mechanismextends along the Z direction. In the embodiment, the rotation axis AX corresponds to a rotation axis of the first memberand a rotation axis of the second member. Note that in the present disclosure, the “cylindrical shape” includes a solid cylindrical shape and a hollow cylindrical shape. Further, hereinafter, a direction along the rotation axis AX is also referred to as a rotation axis AX direction.

A circumferential direction DC of the torque transmission mechanismcorresponds to a circumferential direction of the first memberand a circumferential direction of the second member. In the present disclosure, the circumferential direction DC is defined as a counterclockwise direction when the torque transmission mechanismis viewed from the +Z direction side. In addition, in the following description, unless otherwise specified, “counterclockwise” means counterclockwise when the torque transmission mechanismis viewed from the +Z direction side. Substantially the same applies to “clockwise”.

The first memberhas a cylindrical shape. More specifically, the first memberhas a hollow cylindrical shape. The first memberis disposed such that the axial direction of the first memberis along the Z direction. In the embodiment, the first memberis disposed innermost in a horizontal direction among portions of the torque transmission mechanism. The first memberis configured to be rotatable around the rotation axis AX of the torque transmission mechanism. As illustrated in, the first memberincludes an outer peripheral surface. The outer peripheral surfaceis provided with a first groove. The first groovehas a zigzag shape extending around and going around the rotation axis AX above the outer peripheral surface. In the present specification, the “zigzag shape” means a shape, while reciprocating one or more times in a certain direction, extending so as to advance in a direction orthogonal to the certain direction. That is, the zigzag shape has one or more turning points. The turning points of the zigzag shape may be sharp or rounded. Details of the first groovewill be described below.

As illustrated in, the second memberhas an annular shape surrounding the first member. That is, an inner diameter of the second memberis larger than an outer diameter of the first member. The second memberis disposed such that the axial direction of the second memberis along the Z direction. In the embodiment, the second memberis disposed outermost in the horizontal direction among the portions of the torque transmission mechanism. The second memberis configured to be rotatable around the rotation axis AX. As illustrated in, the second memberincludes an inner peripheral surface. The inner peripheral surfaceis provided with a second groove. The second groovehas a zigzag shape extending around and going around the rotation axis AX above the inner peripheral surface. Details of the second groovewill be described below.

is a cross-sectional view taken along line III-III in.is a cross-sectional view taken along line IV-IV in. As illustrated in, the first rolling memberis disposed in the first grooveand in the second groovebetween the first memberand the second member. The first rolling memberis configured to be rollable in the first grooveand in the second groove. Specifically, the first rolling memberrolls in the first grooveand in the second grooveso as to be disposed at a position where the first grooveand the second grooveintersect with each other when viewed along a radial direction of the torque transmission mechanism. When the first rolling memberrolls in the first groove, the first rolling memberand the first membermove relative to each other. Further, when the first rolling memberrolls in the second groove, the first rolling memberand the second membermove relative to each other. The first rolling memberin the embodiment has a spherical shape. The first rolling memberis configured as a so-called steel ball, for example, and is made of stainless steel, steel, or the like. As described below, the first rolling membertransmits torque between the first memberand the second member.

In the embodiment, the first rolling membersinclude a rolling memberA, a rolling memberB, a rolling memberC, a rolling memberD, and a rolling memberE. When the rolling members from the rolling membersA toE are not distinguished from each other, each of the rolling members is simply referred to as the first rolling member. The rolling membersA,B,C,D, andE are disposed in this order in the circumferential direction DC when the torque transmission mechanismis viewed from the +Z direction side.

As illustrated in, the first regulating memberis disposed between the first memberand the second member. In the embodiment, the first regulating memberhas a hollow cylindrical shape as a whole. The first regulating memberis disposed such that an axial direction of the first regulating memberis along the Z direction.

The first regulating memberincludes a main body portion, a first flange portion, and a second flange portion. The main body portionis a portion of the first regulating memberthat is disposed inside an annulus of the second member. The first flange portionis an annular flange portion constituting a lower end portion of the first regulating member. The second flange portionis an annular flange portion constituting an upper end portion of the first regulating member. As illustrated in, the first flange portionis not disposed inside the annulus of the second member, but is disposed below a lower end portion of the first memberand a lower end portion of the second member. In substantially the same manner, the second flange portionis disposed above an upper end portion of the first memberand an upper end portion of the second member. In the embodiment, the first flange portionis formed integrally with the main body portion. The second flange portionis configured as a cap being a body separate from the main body portion, and is fixed to the main body portionvia a bolt. An outer diameter of the main body portionis smaller than the inner diameter of the second member. On the other hand, outer diameters of the first flange portionand the second flange portionare larger than an inner diameter of a second portion. An inner diameter of the main body portionis larger than the outer diameter of the first member. On the other hand, inner diameters of the first flange portionand the second flange portionare smaller than the outer diameter of the first member. The inner diameter of the first flange portionis substantially the same as the inner diameter of the second flange portion. The outer diameter of the first flange portionis substantially the same as the outer diameter of the second flange portion.

As illustrated in, the main body portionincludes a slit portion. In the embodiment, the main body portionincludes five slit portions. An opening portion is configured so as to extend along the rotation axis AX, that is, along the Z direction. A wall portionof the main body portionis disposed between openings of the slit portions. The wall portioncorresponds to a wall in the circumferential direction DC among walls defining the opening of the slit portion. As illustrated in, in the embodiment, a lower end of the opening of the slit portionis defined by the first flange portion. Additionally, as illustrated in, an upper end of the opening of the slit portionis defined by the second flange portion. An opening width of the opening of the slit portionin the circumferential direction DC is slightly larger than a diameter of the first rolling member. Further, an opening length of the slit portionin the Z direction is larger than the opening width of the slit portion.

The first regulating memberincludes a first regulating portion. The first regulating portionallows movement of the first rolling memberalong the rotation axis AX, that is, movement in the Z direction. On the other hand, the first regulating portionregulates movement of the first rolling memberaround the rotation axis AX. In the embodiment, the first regulating portionincludes a regulating portionA, a regulating portionB, a regulating portionC, a regulating portionD, and a regulating portionE. Hereinafter, when the regulating portionsA toE are not distinguished from each other, each regulating portion is simply referred to as the first regulating portion. Further, the first regulating portionis also simply referred to as a regulating portion.

Specifically, in the embodiment, the first regulating portionincludes the above-described slit portion, and achieves the allowance and regulation of movement of the first rolling memberby the slit portion. For example, the rolling memberA is disposed in the slit portionof the regulating portionA. As a result, movement of the rolling memberA in the Z direction along the slit portionis allowed. On the other hand, movement of the rolling memberA around the rotation axis AX is regulated by the wall portiondefining the slit portion. Similarly, the rolling membersB toE are disposed in the slit portionsof the regulating portionsB to the regulating portionE, respectively. Note that the number of first rolling membersmay be determined in consideration of, for example, strength of the first regulating member. Specifically, as the number of first rolling membersincreases, a total opening area of the slit portionsin the first regulating memberincreases, and the strength of the first regulating membermay decrease. The number of first rolling membersmay be set to a number small enough to suppress such a decrease in strength.

The first bearing portionis disposed between the first memberand the first regulating member. The first bearing portionholds the first memberso as to be rotatable around the rotation axis AX with respect to the first regulating member. The first bearing portionis configured with various bearings such as a ball bearing and a needle bearing, for example. In the embodiment, two first bearing portionsare provided. The first bearing portionsare press-fitted and fixed to an outer side of the upper end portion and an outer side of the lower end portion of the first member, respectively, and pivotally support the upper end portion and the lower end portion of the first member, respectively. The first bearing portionon the lower end portion side of the first memberis disposed inside the main body portionso as to be in contact with an upper surface of the first flange portion. The first bearing portionon the upper end portion side of the first memberis disposed inside the main body portionso as to be in contact with a lower surface of the second flange portion. As a result, while movement of the first memberin the Z direction with respect to the first regulating memberis regulated, the first memberis held so as to be rotatable with respect to the first regulating member.

The second bearing portionis disposed between the second memberand the first regulating member. The second bearing portionholds the second memberso as to be rotatable around the rotation axis AX with respect to the first regulating member. Similarly to the first bearing portion, the second bearing portionis configured with various bearings, for example. In the embodiment, two second bearing portionsare provided. The second bearing portionsare press-fitted and fixed to an inner side of the upper end portion and an inner side of the lower end portion of the second member, respectively, and pivotally support the upper end portion and the lower end portion of the second member, respectively. The second bearing portionon the lower end portion side of the second memberis disposed outside the main body portionso as to be in contact with the upper surface of the first flange portion. The second bearing portionon the upper end portion side of the second memberis disposed outside the main body portionso as to be in contact with the lower surface of the second flange portion. As a result, while movement of the second memberin the z direction with respect to the first regulating memberis regulated, the second memberis held so as to be rotatable with respect to the first regulating member.

is a first explanatory view of the torque transmission mechanism.illustrates an outer peripheral surfaceand an inner peripheral surface. The outer peripheral surfacecorresponds to the spread outer peripheral surface. The inner peripheral surfacecorresponds to the spread inner peripheral surface.illustrates a state in which the outer peripheral surfaceand the inner peripheral surfaceare overlaid with each other. In addition, in, each first regulating portionis schematically illustrated by a broken line. In addition, in, each first rolling memberis schematically illustrated by hatching.

illustrates an angle θ at the outer peripheral surfaceand the inner peripheral surface. The angle e increases as a distance in the circumferential direction DC increases. An angular position Afor 0 degrees and an angular position Afor 360 degrees illustrated inare positions identical to each other. In the embodiment, the regulating portionA is positioned at the angular position A. In, in order to make the technique easier to understand, the rolling memberA and the regulating portionA are illustrated in each of a vicinity of the angular position Aand a vicinity of the angular position A. However, in actuality, the number of rolling memberA and the number of regulating portionA are one.

In, the first grooveis indicated by a thick line. The first groovehas a closed ring shape that goes around the outer peripheral surfacealong the circumferential direction DC. The first grooveas a whole has a periodic wave shape that advances along the circumferential direction DC while reciprocating on the outer peripheral surfacein the Z direction. That is, when the first grooveis regarded as a wave, a traveling direction of the first grooveis a direction along the circumferential direction DC, and a vibration direction of the first grooveis the Z direction. Specifically, the first groovehas a triangular wave shape. The first groovehas one period. That is, the first grooveincludes one mountain portionand one valley portionThe mountain portionand the valley portionhave a pointed shape. A position of each mountain portionin the Z direction is substantially the same. Further, a position of each valley portionin the Z direction is substantially the same. That is, when the first grooveis regarded as a wave, amplitude of the first grooveis substantially constant. Each of the mountain portion and the valley portion corresponds to the turning point of the zigzag shape described above. Note that in the embodiment, the mountain portion is positioned on the +Z direction side of the valley portion. In other embodiments, the positional relationship between the mountain portion and the valley portion may be reversed.

The second groovehas a closed ring shape that goes around the inner peripheral surfacein the circumferential direction DC. The second grooveas a whole has a periodic wave shape that advances along the circumferential direction DC while reciprocating on the inner peripheral surfacein the Z direction. That is, when the second grooveis regarded as a wave, a traveling direction of the second grooveis a direction along the circumferential direction DC, and a vibration direction of the second grooveis the Z direction. Specifically, the second groovehas a triangular wave shape. The second groovehas a period different from that of the first groove. Specifically, the second groovehas twelve periods. That is, the second grooveincludes twelve mountain portionsand twelve valley portionsThe mountain portionand the valley portionhave a pointed shape. The position of each mountain portionin the Z direction is substantially the same, and is substantially the same as the position of each mountain portionin the Z direction. Further, the position of each valley portionin the Z direction is substantially the same as each other, and is substantially the same as the position of each valley portionin the Z direction. That is, when the second grooveis regarded as a wave, amplitude of the second grooveis substantially constant and substantially the same as the amplitude of the first groove.

In the embodiment, in the torque transmission mechanism, one of the first memberand the second memberis used as an input shaft, and another is used as an output shaft. Hereinafter, operation of the torque transmission mechanismwhen the first memberis used as the input shaft will be described.

is a second explanatory view of the torque transmission mechanism.illustrates a state in which the first memberas the input shaft rotates in the circumferential direction DC around the rotation axis AX by a rotation angle θfrom the state illustrated in. In the example in, the rotation angle θis 60 degrees.

As illustrated in, when the first memberrotates around the rotation axis AX, each first rolling memberrolls in the first grooveand in the second groove. To be specific, by the rotation of the first member, the first rolling memberrolls on a path Ptin the first groove. The path Ptis such a path that a length of the path Ptin the circumferential direction DC corresponds to the rotation angle θ. To be specific, the path Ptis such a path that a position of the first rolling memberbefore the first memberstarts to rotate is a start point S, and a position advanced from the start point in the circumferential direction DC by an amount corresponding to the rotation angle θis an end point E, in the first groove. In, as an example of the path Pt, the path Ptwith respect to the rolling memberA is indicated by dot-pattern hatching. When the first rolling memberrolls on the path Pt, the movement of the first rolling memberaround the rotation axis AX is regulated, so that the first rolling membermoves only in the Z direction along the first groove. As a result, while a position of the first rolling memberin the circumferential direction DC does not change, a position of the first rolling memberin the Z direction changes in accordance with a position of the path Ptin the Z direction. In addition, the first rolling memberrolls on a path Ptin the second groovewhile moving in the Z direction as described above, to transmit torque to the second membervia the second groove, and rotates the second memberaround the rotation axis AX. The path Ptis such a path that a positional change of the first rolling memberin the rotation axis AX direction when passing through the path Ptis the same as a positional change of the first rolling memberin the rotation axis AX direction when passing through the path Pt. In, as an example of the path Pt, the path Ptwith respect to the rolling memberA is indicated by dot-pattern hatching. As a result, the second memberrotates around the rotation axis AX by a rotation angle θcorresponding to a length of the path Ptin the circumferential direction DC, that is, a length between a start point Sand an end point Eof the path Ptin the circumferential direction DC. A ratio of the rotation angle θto the rotation angle θcorresponds to a ratio of a period Tof the first grooveto a period Tof the second groove. That is, a deceleration ratio RRin this case corresponds to a value obtained by dividing the period Tby the period T. Note that as indicated by a white arrow in, it can be said that the first rolling membersuch as the rolling memberA moves in the first grooveand in the second grooverelative to the first memberand the second memberin a direction opposite to a rotation direction of the first memberand the second member.

Operation of the torque transmission mechanismwhen the second memberis used as the input shaft is substantially the same as the operation of the torque transmission mechanismwhen the first memberis used as the input shaft. In this case, the first rolling memberrolls in the first grooveby rotation of the second member, to transmit torque to the first membervia the first groove. Further, a deceleration ratio RRin this case corresponds to a value obtained by dividing the period Tby the period T. That is, in this case, rotation input to the torque transmission mechanismvia the second memberis accelerated via the first memberand output.

As illustrated in, the respective first rolling membersare disposed at crossing positions CP where the first grooveand the second grooveintersect with each other when viewed along a radial direction DR. The crossing positions CP include a first crossing position CP, a second crossing position CP, a third crossing position CP, and a fourth crossing position CP. The first crossing position CPis a position where a first positive portion Pand a second positive portion Pintersect with each other. The first positive portion Pis a portion of the first groovethat extends from the valley portiontoward the mountain portionto a forward direction side in the circumferential direction DC. The second positive portion Pis a portion of the second groovethat extends from the valley portiontoward the mountain portionto the forward direction side in the circumferential direction DC. The second crossing position CPis a position where a first negative portion Nand a second negative portion Nintersect with each other. The first negative portion Nis a portion of the first groovethat extends from the mountain portiontoward the valley portionto the forward direction side in the circumferential direction DC. The second negative portion Nis a portion of the second groovethat extends from the mountain portiontoward the valley portionto the forward direction side in the circumferential direction DC. The third crossing position CPis a position where the first positive portion Pand the second negative portion Nintersect with each other. The fourth crossing position CPis a position where the first negative portion Nand the second positive portion Pintersect with each other. Note that each of the first positive portion Pand the first negative portion Nincludes a peak of the mountain portionand a peak of the valley portionFurther, each of the second positive portion Pand the second negative portion Nincludes a peak of the mountain portionand a peak of the valley portion

In the embodiment, each first rolling memberis disposed at the first crossing position CPor the second crossing position CP. As a result, the rotation directions of the first memberand the second membercoincide with each other. Note that in the other embodiments, each first rolling membermay be disposed at the third crossing position CPor the fourth crossing position CP. In this case, the rotation direction of the first memberand the rotation direction of the second memberare opposite to each other.

According to the torque transmission mechanismin the embodiment described above, the first rolling memberdisposed in the first grooveof the first memberand in the second grooveof the second memberis configured to be rollable in the first grooveand in the second groove. In the first grooveand in the second groove, the movement of the first rolling memberalong the rotation axis AX is allowed, and the movement of the first rolling memberaround the rotation axis AX is regulated. Therefore, torque can be transmitted between the first memberand the second memberwithout using a pin for torque transmission.

In addition, in the embodiment, the number of mountain portionsand the number of valley portionsof the first grooveare different from the number of mountain portionsand the number of valley portionsof the second groove, respectively. According to this aspect, it is possible to decelerate a rotation speed between the first memberand the second memberin accordance with the number of mountain portionsand the number of valley portionsof the first grooveand the number of mountain portionsand the number of valley portionsof the second groove. That is, the rotation speed can be decelerated between the first memberand the second memberin accordance with a difference between the period Tof the first grooveand the period Tof the second groove. Further, in the embodiment, various deceleration ratios can be achieved with high flexibility by optionally changing the combination of the period Tand the period T.

In addition, in the embodiment, the first rolling memberhas a spherical shape. Therefore, the first rolling membercan be more smoothly rolled in the first grooveand in the second groove. Additionally, as a result, wear of the first member, the second member, the first rolling member, and the first regulating membercan be suppressed.

In addition, in the embodiment, the first rolling memberincludes one rolling memberA and another rolling memberB. With this configuration, torque can be transmitted between the first memberand the second memberusing the rolling memberA and the rolling memberB. Therefore, for example, it is possible to reduce a load for each first rolling memberas compared with an embodiment in which the rolling memberA is provided.

In addition, as in the embodiment, since the plurality of first rolling membersare provided, it is easy to uniquely determine a rotation direction of the second memberwith respect to the first memberor a rotation direction of the first memberwith respect to the second member. To be specific, for example, in a case where only the rolling memberA is provided, when the rolling memberA approaches the mountain portionor the valley portionof the second groovedue to the rotation of first memberas the input shaft, the rolling memberA may advance in the second groovetoward either one side or another side in the circumferential direction DC. As a result, since the second membermay rotate both in the forward direction of the circumferential direction DC and in a backward direction of the circumferential direction DC, there is a possibility that a phenomenon occurs in which the second memberreciprocates in a closed space in the circumferential direction DC. Such a phenomenon is likely to occur particularly when the rotation speed of the first memberor the second memberis low. Note that such a phenomenon may also similarly occur when the second memberis used as the input shaft. On the other hand, in a case where the rolling memberB is provided in addition to the rolling memberA, for example, when the rolling memberA approaches the mountain portionor the valley portionthe rolling memberB can be positioned at a portion other than the mountain portionand the valley portionof the second groove. In this case, since a movement direction of the rolling memberB in the second grooveis uniquely determined, the movement direction of the rolling memberB in the second grooveand the rotation direction of the second memberare also uniquely determined.

Further, in the embodiment, it is possible to more smoothly rotate the first memberwith respect to the first regulating membervia the first bearing portiondisposed between the first memberand the first regulating member.

Further, in the embodiment, it is possible to more smoothly rotate the second memberwith respect to the first regulating membervia the second bearing portiondisposed between the second memberand the first regulating member.

In addition, in the embodiment, each of the first grooveand the second groovehas a triangular wave shape. Therefore, at each position in the first grooveand each position in the second groove, an amount of movement of the first rolling memberin the Z direction per unit rotation angle of each of the first memberand the second memberis substantially constant, so that the first membercan be more stably rotated with respect to the second memberor the second membercan be more stably rotated with respect to the first member. As a result, more stable deceleration can be achieved between the first memberand the second member. In addition, as compared to a case where the first grooveor the second groovehas a zigzag shape having a rounded mountain portion or a valley portion, such as a sinusoidal shape, for example, it is possible to further increase torque transmission efficiency in the mountain portion or the valley portion. As a result, torque can be more efficiently transmitted between the first memberand the second member.

is a cross-sectional view schematically illustrating a schematic configuration of a torque transmission mechanismin a second embodiment.is a cross-sectional view taken along line VIII-VIII in.illustrates a cross-section of the torque transmission mechanismtaken along the X direction and the Y direction.illustrates a cross-section of the torque transmission mechanismtaken along the X direction and the Z direction. As illustrated in, in the embodiment, unlike the first embodiment, an outer peripheral surfaceof a second memberis provided with a third groove. Further, the torque transmission mechanismfurther includes a third member, one or more second rolling members, and a second regulating member. Points for the torque transmission mechanismin the embodiment that are not particularly described are the same as those in the first embodiment. Note thatillustrate an example in which each of the number of first rolling membersand the number of second rolling membersis four. In addition, in, each of the first groove, the second groove, and the third grooveis schematically illustrated by a broken line. In addition, in, for example, the members such as the first bearing portionand the second bearing portionare omitted as appropriate.

The third groovehas a zigzag shape extending around and going around the rotation axis AX on the outer peripheral surface. The third grooveis configured in substantially the same manner as the first groove, for example. In the embodiment, the third groovehas a closed ring shape that goes around the outer peripheral surfacein the circumferential direction DC. The third grooveas a whole has a periodic wave shape that advances along the circumferential direction DC while reciprocating along the rotation axis AX on the outer peripheral surface. Specifically, the third groovehas a triangular wave shape. A period Tof the third groovemay be the same as or different from the period Tor the period T. The period Tin the embodiment is one. A position of each mountain portion in the Z direction of the third grooveis substantially the same. Further, a position of each valley portion in the Z direction of the third grooveis substantially the same.

As illustrated in, the third memberhas an annular shape surrounding the second memberThat is, an inner diameter of the third memberis larger than an outer diameter of the second member. In the embodiment, the third memberis disposed outermost in the horizontal direction among respective portions of the torque transmission mechanismThe third memberis configured to be rotatable around the rotation axis AX. As illustrated in, the third memberincludes an inner peripheral surface. The inner peripheral surfaceis provided with a fourth groove.

The fourth groovehas a zigzag shape extending around and going around the rotation axis AX on the inner peripheral surface. The fourth grooveis configured in substantially the same manner as the second groove, for example. The fourth groovehas a closed ring shape that goes around the inner peripheral surfacein the circumferential direction DC. The fourth grooveas a whole has a periodic wave shape that advances along the circumferential direction DC while reciprocating along the rotation axis AX on the inner peripheral surface. Specifically, the fourth groovehas a triangular wave shape. The fourth groovehas a period Tdifferent from the period T. That is, the number of mountain portions and the number of valley portions of the third grooveare different from the number of mountain portions and the number of valley portions of the fourth groove, respectively. The period Tmay be the same as or different from the period Tor the period T. In the embodiment, a magnitude relationship between the period Tand the period Tis the same as a magnitude relationship between the period Tand the period T. To be specific, the period Tin the embodiment is twelve. A position of each mountain portion of the fourth groovein the Z direction is substantially the same, and is substantially the same as the position of each mountain portion of the third groovein the Z direction. Further, a position of each valley portion of the fourth groovein the Z direction is substantially the same, and is substantially the same as the positions of each valley portion of the third groovein the Z direction.

The second rolling memberis configured in substantially the same manner as the first rolling member, for example. The second rolling memberis disposed in the third grooveand in the fourth groovebetween the second memberand the third member. The second rolling memberis configured to be rollable in the third grooveand in the fourth groove. To be specific, the second rolling memberrolls in the third grooveand in the fourth grooveso as to be disposed at a position where the third grooveand the fourth grooveintersect with each other when viewed along a radial direction of the torque transmission mechanismThe second rolling memberin the embodiment has a spherical shape similarly to the first rolling member. The second rolling membertransmits torque between the second memberand the third member.

The second regulating memberis configured in substantially the same manner as the first regulating member, for example. In the embodiment, the second regulating memberhas a hollow cylindrical shape as a whole. The second regulating memberis disposed between the second memberand the third member. The second regulating memberallows movement of the second rolling memberalong the rotation axis AX, and regulates movement of the second rolling memberaround the rotation axis AX. Note that, for example, substantially the same bearing portion as the first bearing portionor the second bearing portionmay be disposed between the second regulating memberand the second memberand between the second regulating memberand the third member. That is, such a bearing portion holds the second memberor the third memberso as to be rotatable around the rotation axis AX with respect to the second regulating member.

In the embodiment, similarly to the first embodiment, deceleration via the first rolling memberis achieved between the first memberand the second memberFurthermore, in the embodiment, deceleration via the second rolling memberis achieved between the second memberand the third member. The behavior of the third memberwith respect to the second memberis substantially the same as the behavior of the second memberwith respect to the first member. For example, when the first memberis used as the input shaft, the deceleration ratio RRis achieved between the first memberand the second memberand a deceleration ratio RRis achieved between the second memberand the third member. The deceleration ratio RRcorresponds to a value obtained by dividing the period Tby the period T. As a result, a deceleration ratio RRis achieved between the first memberas the input shaft and the third memberas the output shaft. The deceleration ratio RRcorresponds to a product of the deceleration ratio RRand the deceleration ratio RR. Further, when the third memberis used as the input shaft, a deceleration ratio RRis achieved between the third memberand the second memberand the deceleration ratio RRis achieved between the second memberand the first member. The deceleration ratio RRcorresponds to a value obtained by dividing the period Tby the period T. As a result, a deceleration ratio RRis achieved between the third memberas the input shaft and the first memberas the output shaft. The deceleration ratio RRcorresponds to a product of the deceleration ratio RRand the deceleration ratio RRThat is, in this case, rotation input to the torque transmission mechanismis accelerated and output.

According to the torque transmission mechanismin the second embodiment described above, the second rolling memberdisposed in the third grooveprovided at the outer peripheral surfaceof the second memberand in the fourth grooveprovided at the inner peripheral surfaceof the third membersurrounding the second memberis configured to be rollable in the third grooveand in the fourth groove. The movement of the second rolling memberalong the rotation axis AX is allowed, and the movement of the second rolling memberaround the rotation axis AX is regulated. The number of mountain portions and the number of valley portions of the third grooveare different from the number of the mountain portions and the number of valley portions of the fourth groove, respectively. With this configuration, it is possible to decelerate a rotation speed in a stepwise manner between the first memberand the second member, and between the second memberand the third member. Therefore, for example, a higher deceleration ratio can be achieved without excessively increasing the period of the second grooveor the fourth groove. As a result, for example, it is possible to suppress an increase in size of the second memberor the third memberwith an increase in the period of the second grooveor the fourth groove, and thus it is possible to achieve a higher deceleration ratio while configuring the torque transmission mechanismin a more space-saving manner. In addition, for example, it is possible to suppress an excessive reduction in size of the first rolling memberor the second rolling memberwith an increase in the period of the second grooveor the fourth groove, therefore, it is possible to achieve a higher deceleration ratio while suppressing a decrease in durability of the torque transmission mechanismNote that in the other embodiment, for example, a fourth member may be provided outside the third memberso as to achieve further stepwise deceleration.

is a cross-sectional view schematically illustrating a schematic configuration of a torque transmission mechanismin a third embodiment. In substantially the same manner as,illustrates a cross-section of the torque transmission mechanismalong the X direction and the Z direction. In the embodiment, unlike the first embodiment, an outer peripheral surfaceof a first memberis provided with a first corresponding groove. Additionally, an inner peripheral surfaceof a second memberis provided with a second corresponding groove. One or more third rolling memberare disposed in the first corresponding grooveand in the second corresponding groove. Further, the first regulating memberincludes a second regulating portion. Points for the torque transmission mechanismin the embodiment that are not particularly described are the same as those in the first embodiment.

The first corresponding grooveis arranged side by side with the first groovein the Z direction. In the embodiment, the first corresponding grooveis disposed on the +Z direction side of the first groove. The first corresponding grooveis a groove corresponding to the first grooveand has a zigzag shape corresponding to the first groove. Specifically, the first corresponding groovehas the same period as the first groove. That is, the first corresponding groovehas a periodic wave shape including the same number of mountain portionsand valley portionsas the mountain portionsand valley portionsof the first groove. In the embodiment, the first grooveand the first corresponding grooveare disposed such that the mountain portionof the first grooveand the valley portionof the first corresponding grooveface each other. Note that, in the first memberfor example, a portion provided with the first grooveand a portion provided with the first corresponding groovemay be configured as bodies separated from each other, and both the portions stacked at each other may be fixed to each other to configure the first member

The second corresponding grooveis disposed side by side with the second groovein the Z direction. In the embodiment, the second corresponding grooveis disposed on the +Z direction side of the second groove. The second corresponding grooveis a groove corresponding to the second grooveand has a zigzag shape corresponding to the second groove. Specifically, the second corresponding groovehas the same period as the second groove. That is, the second corresponding groovehas a periodic wave shape including the same number of mountain portionsand valley portionsas the mountain portionsand valley portionsof the second groove. Further, the number of mountain portionsand the number of valley portionsof the first corresponding grooveare different from the number of mountain portionsand the number of valley portionsof the second corresponding groove, respectively. In the embodiment, the second grooveand the second corresponding grooveare disposed such that the mountain portionof the second grooveand the valley portionof the second corresponding grooveface each other. Note that, in substantially the same manner as the first memberfor example, the second membermay be configured such that a portion provided with the second grooveand a portion provided with the second corresponding grooveare separate bodies.

The third rolling memberis configured to be rollable in the first corresponding grooveand in the second corresponding groove. The third rolling memberis configured, for example, in substantially the same manner as the first rolling member. The third rolling membertransmits torque between the first memberand the second memberin substantially the same manner as the first rolling member. The second regulating portionallows movement of the third rolling memberalong the rotation axis AX, and regulates movement of the third rolling memberaround the rotation axis AX. The second regulating memberis configured in substantially the same manner as the first regulating portion, for example. To be specific, in the embodiment, the first regulating memberis provided with a slit portionextending from the first grooveand the second grooveto the first corresponding grooveand the second groovein the Z direction, and allowance and regulation of the movement of the first rolling memberand the third rolling memberare achieved by the slit portionNote that in the other embodiment, for example, the first regulating portionand the second regulating portionmay have respective separate slit portions, and the allowance and regulation of the movement of the first rolling memberand the third rolling membermay be achieved by the respective slit portions.